Neutral Connection For Balanced Load 2

[341968]

Could you please guide me that
I have LV transformer Star connected.
Only 3-phase are going to panel.
Star point(Neutral bus) of TR is only solidly grounded.
Panel has neutral bus BUT empty (No cables), No Ground.
Reason not being using Neutral is completely balanced load (4-Motors DOL and 8-Motors through VFD Each 90KW).
My Question: Can I make connection (Cabling) between TR neutral and Main panel Neutral, as I need 230V for ACB motor. That I want to turn it into TNS system. Doing so any adverse effects? Any recommendation?

 

[davidbeach]

An arcing fault in switchgear will start as 1LG, but within a cycle or a cycle and a half it has another phase and almost immediately has become 3-phase. Once it's 3-phase the presence of a grounded anything doesn't much matter. I haven't seen any 480V arc fault records, but in 15kV and 35kV class equipment the expanding plasma cloud from the original fault doesn't take long to make contact with the other two phases. Given the number and area of grounded surfaces, the addition of a neutral would seem to have minimal impact on arc flash initiation risk and no impact on the results. That's why the arc-flash standards don't consider anything other than 3-phase for enclosed faults.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

Thanks for the information, David. I'll accept that.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[341968]

No, you should NOT connect any load to the Board Neutral bar, even the utility Neutral is earthed. Take note that (in this case) there is No connection between the utility Neutral to the Board Neutral, which is "floating" and is isolated from earth.
Che Kuan Yau AGREE Please see attached pdf page 16, Through an aux Tr. Neutral has been created and all panel single load is connected with that. Similarly the two trs. give line and neutral for ACB spring charging Motor. Only what I have to do to disconnect the 400V lines from out put of the ACB to the Input / Tr. side. Rest panel will stay exactly in same condition. Neutral bus and Earthing bus are already isolated.

 

[341968]

Here page 16-17-18/21

 

[che12345]

Mr 341968 (Electrical)(OP)22 May 23 05:46
"....Please see attached pdf page 16, Through an aux Tr. Neutral has been created and all panel single load is connected with that. Similarly the two trs. give line and neutral for ACB spring charging Motor...".
My personal opinion:
1. Incoming (52IL) placed at A1 extreme LHS is a bad decision. Should place it at the middle such that the current will be about half on each side.
2. I don't see any "page" indication on the drawings.
3. I noticed you had added TR1, TR2 4kVA and TR3 20kVA 400/230V single-phase step-down transformers in A12 cubicle.
Attention: a) These transformer secondaries shall terminate on their respective n1, n2 and n3 terminal blocks for their respective loads. In addition, n1,n2 and n3 SHALL be earthed to the earthing bar, which is in good contact with the Board frame and earthed by the local electrodes.
b) Do NOT connect the n1,2, 3 to the Board Neutral. Leave it "floating" alone, isolated from earth; NOT connected to the utility earthed Neutral.
c) The Board is designed for TN-S. But you don't have a PE and N from the utility to the Board. Therefore, it is NOT a TN-S system according to the design. Even you earth the Board locally, the Board is NOT a TT system, as there is NO connection from the utility earthed Neutral to the Board Neutral, which is "floating", isolated from earth.
Che Kuan Yau (Singapore)

 

[341968]

Thanks all for your technical expertise shared. Please see attached report I have finally submitted. Client intension to go with Inverter option. Kindly advice how much watt inverter would be enough for spring charging motor of ACB. I have proposed 1000W I believe it very much oversized.